In a conventional manufacturing process of pulp production from wood chips, flows of steam are inputted into various vessels. Due to the nature of the substrates present inside the vessel, such as wood chips and pulp, the steam that passes through the substrates will carry wood fibers and other light weight impurities that are not easily condensable. Consequently, the impurities will rise with the steam and other non-condensable gases, and attach to the screen basket or screen (also referred to as a strainer or a filter for use in any location where steam is being screened, strained or filtered) of a vessel, such as steam relief vessel, at the steam relief valve, creating clogs in the filtering or screening process. The steam is released through a steam relief vessel that contains a steam relief screen basket (screen basket) to filter out the impurities and fibers that arise with the steam and non-condensable gases before the vapor exits the vessel. The screen basket is typically located within a steam relief strainer (or steam relief chamber) within the vessel. The steam relief vessel is present in machines such as steaming vessels and chip bins used in the kraft pulping process. An example of a conventional screen basket used in such a practice is a steam relief strainer (usually cylindrical in shape) that is placed inside the steam relief vessel.
On a steam relief vessel, there is at least one exit steam relief valve in place that allows the steam to be released from the vessel. Conventional means of clearing a steam relief screen basket of impurities include shutting off the relief valve periodically, and releasing a burst of steam backward through the steam relief screen basket at a pressure higher than the pressure in the vessel. This practice is called the “steam blow-back method.”
Conventionally, the blow-back steam is obtained through an extension of the steam pipe that supplies the steam to the vessel. The blow-back steam is at a pressure higher than the pressure in the vessel before it is released through the steam nozzles into the steam relief chamber. During the procedure, the steam relief valve is normally closed: no steam is relieved out of the vessel and the pressure is allowed to build up inside the vessel. Because of the pressure buildup from the closing of the relief valve and the pressured blow-back steam, the procedure is performed periodically and infrequently for a short period of time.
This blow-back action of the conventional method creates openings in a layer of impurities that collects on the screen basket, which temporarily clears part of the screen basket of impurities. The openings allow for further filtering until another layer of impurities builds up again on the screen basket surface. For example, such a cleaning procedure performed on the cylindrical steam relief screen basket would require numerous steam nozzles to be mounted on the steam relief chamber that houses the cylindrical screen basket. The blow-back steam would reenter the steam relief chamber through the steam nozzles, and create openings in the area of the screen basket that is directly in line with the steam nozzles. The openings allow for further filtering until the opening is covered with impurities, at which time yet another blow-back cycle must be initiated.